1. You must hand in your compositions before Friday
-> Your compositions must be handed before Friday

 2. They might postponel the excursion until Saturday .
-> The excursion might be postponed until Saturday

3. An expert should check these machines regularly
-> These machines should be checked regularly by an expert

 4. You must attach a birth certificate to the application
-> A birth certificate must be attached to the application

. 5. They have known him well 
-> He has been known well by them

6. They shouldn't cut the flowers in this garden 
-> The flowers in this garden shouldn't be cut